1. Field of the Invention
The present invention relates to green light-emitting compounds. More particularly, the present invention relates to iridium-based luminescent compounds having phenylpyridine moieties with an organosilicon group, and organic electroluminescence devices using the compounds as color-producing materials.
2. Discussion of the Related Art
Generally, electroluminescence (EL) devices are self-emissive display devices and are advantageous in terms of broad viewing angle, high contrast, and rapid response time. Such EL devices are classified into inorganic EL devices and organic EL devices according to the kind of materials for the formation of emitter layers. Organic EL devices have excellent luminance, driving voltage and response rate characteristics and easily produce various colors, when compared to inorganic EL devices.
General organic EL devices comprise a substrate, an anode, a hole injecting layer, a hole transport layer, a light-emitting layer, an electron transport layer, and a cathode formed in this order from the bottom. The hole transport layer, the light-emitting layer, and the electron transport layer are organic thin films made of organic compounds.
The fabrication of an organic EL device will be briefly explained below.
(1) First, an anode material is coated on a transparent substrate to form an anode. Indium tin oxide (ITO) is mainly used as the anode material.
(2) A hole injecting layer (HIL) is formed to a thickness of 10˜30 nm on the anode. Copper phthalocyanine (CuPc) is mainly used as a material for the hole injecting layer.
(3) A hole transport layer is formed on the hole injecting layer. The hole transport layer is formed by depositing 4,4′-bis[N-(1-naphthyl)-N-phenylamino]-biphenyl (NPB) to a thickness of about 30 nm to about 60 nm on the hole injecting layer.
(4) An organic light-emitting layer is formed on the hole transport layer. If needed, a dopant is added to a material for the organic light-emitting layer. For green light emission, tris(8-hydroxyquinoline aluminum) (Alq3) as a material for the organic light-emitting layer is deposited to a thickness of about 30 nm to about 60 nm on the hole transport layer, and N-methylquinacridone (MQD) is mainly used as a dopant.
(5) An electron transport layer (ETL) and an electron injecting layer (EIL) are sequentially formed on the organic light-emitting layer. Alternatively, an electron injecting/transport layer is formed on the organic light-emitting layer. In the case of green light emission, since Alq3 has superior electron transport ability, the use of the electron injecting/transport layer may be unnecessary.
(6) A cathode material is coated on the electron injecting layer, and finally the resulting structure is covered with a protective film.
The operational principle of the organic EL device having the structure described above is as follows.
When a voltage is applied between the anode and the cathode, holes injected from the anode migrate to the light emitting layer via the hole transport layer while electrons injected from the cathode migrate to the light emitting layer via the electron transport layer. The carriers are recombined with each other in the light emitting layer to form excitons, and then the excitons fall from the excited state to the ground state to allow fluorescent molecules present in the light-emitting layer to emit light, achieving the formation of images.
However, although conventional luminescent compounds that have been used as materials for organic light-emitting layers show superior luminescent properties, there is the disadvantage of poor luminescent efficiency due to triplet-triplet annihilation. Accordingly, there is room for improvement in the efficiency of conventional luminescent compounds.